"Though 'flat design' is a popular meme right now, there is something much, much deeper going on here at Microsoft. With my own lifelong passion for design I immersed myself in the community and got a front-row seat on a journey that has its roots as far back as the late '90s with Encarta's bold use of typography and clean interface. But it truly sprang to life in late 2010 with the launch of Windows Phone and in the last few weeks has advanced even further with Windows 8.1 and Xbox One. I started from the very place I bet you are right now - disbelief that Microsoft is leading the way on design." They really are. If Apple really goes all minimalist and digital (I dislike the term 'flat') with iOS, Microsoft will have taken over the baton. Crazy world indeed.

I don't know if such an app exists under Linux, because I never needed one. KDE apps usually have A LOT of actions that can be assigned to hotkeys (even global hotkeys). Using DBus and a tiny scripted KDE app (for global hotkey support - hotkeys are an integral part of KDE/Qt and thus very easy to implement) I guess one could write such an app for all KDE and probably many Gtk apps. Heck, that what I did for the special case of media players: http://kde-apps.org/content/show.php?content=144437 (a plasma widget that lets you assign global hotkeys for play/pause/next song/previous song which will be sent to whatever media player is currently active - 614 LOC including license header, GUI code and special case code for several buggy players and two different MPRIS API versions)